1) Field of the Invention
This invention relates to a fingerprint data synthesis method and apparatus as well as a computer-readable recording medium on which a fingerprint data synthesis program is recorded for producing fingerprint data to identify an individual. The present invention relates also to a biometric information synthesis method for producing biometric information which uses not only a fingerprint but also other biometric information such as, for example, a palm print, a finger shape, a palm shape, voice, the retina, the iris, a face picture, a dynamic signature, a blood vessel pattern or a keystroke to identify an individual.
2) Description of the Related Art
In recent years, as extensive introduction of the computer into the social system proceeds, the concern is concentrated upon the security. Conventionally, an ID card or a password is used in order to identify the person itself to allow entry into a computer room or utilization of a terminal. However, such identification means still have many subjects to be solved in terms of the security.
Attention is paid to an individual identification technique which makes use of biometric information as means for identifying the person itself which is higher in reliability than the password. Identification of the person itself using biometric information unique to the individual provides very high reliability.
One of several kinds of biometric information which can be utilized for identification of the person itself is a fingerprint. The fingerprint has the two significant characteristics that “it is different among different people” and that “it does not change till the end of the person's life” and is considered powerful measures for identification of the person itself. In recent years, much effort has been directed to investigations and developments on an individual identification system which uses a fingerprint.
A fingerprint is a fine convex and concave geometry at a fingertip of a human being. A connection of convex portions is called ridge or ridgeline. If a ridge is traced, then a point (bifurcation) at which it is bifurcated or another point (end point) beyond which it does not extend anymore is reached. The distribution of such bifurcations or end points is quite different among different people, and therefore, such bifurcations and/or endpoints are called minutiae of a fingerprint. Verification of the distribution condition of such minutiae is used as effective means for specifying an individual. Upon fingerprint verification, coincidence of minutiae in terms of the position, type and direction is detected to discriminate whether or not two fingerprints are the same as each other.
A system for identifying an individual using a fingerprint uses fingerprint images of individuals registered in advance therein. In particular, a user (individual) of the system inputs its fingerprint image by means of a fingerprint scanner, and minutia data (fingerprint data, organism characteristic data) are extracted from the fingerprint image by and registered into the system. Then, when a fingerprint image is inputted using a fingerprint scanner for the object of verification, the system extracts minutia data as fingerprint data from the inputted fingerprint image and verifies the fingerprint data with the fingerprint data registered in advance therein.
Generally, a fingerprint pattern is picked up in the form of a fingerprint image by picking up an image obtained with a fingertip contacted with a special optical system by means of a CCD camera or by detecting only convex portions of the skin by means of an electric capacity sensor. However, depending upon the condition of a fingertip when a fingerprint pattern is picked up, an image which does not exhibit a clear fingerprint such as a blurred fingerprint or a fingerprint image on which ridges look adhered to each other due to sweat may be obtained.
Upon production and registration of registration fingerprint data, if fingerprint data is produced from a fingerprint image on which a fingerprint does not look clearly, then much false minutia information is included in the fingerprint data, which deteriorates the verification performance. Meanwhile, if the inputting area of the fingerprint scanner is not sufficiently large, then the fingerprint pickup area is not fixed every time, which sometimes deteriorates the stability of the verification performance.
Accordingly, fingerprint data produced using a fingerprint image on which a fingerprint pattern looks as clearly as possible is preferably used as registration fingerprint data to be registered in advance in the system. Where such fingerprint data is used, stability of the verification performance and augmentation of the verification success ratio (or lowering of FRR (false rejection rate)) can be anticipated.
Therefore, in order to produce registration fingerprint data, typically it is a conventional practice to pick up a fingerprint image of the same fingertip several times and select one of the resulting fingerprint images on which the fingerprint looks most clearly or to pick up a fingerprint pattern separately for a plurality of divisional portions to obtain a plurality of partial fingerprint images and overlap the partial fingerprint images with each other to produce a fingerprint image on which the fingerprint pattern is exhibited fully over a wide range. Also it is a conventional practice to pick up a fingerprint image of the same fingertip several times, clip, from each of the picked up fingerprint images, a region in which the fingerprint looks clearly and combine the regions clipped from the fingerprint images to produce a fingerprint image of the entire fingerprint.
However, even if a fingerprint image of the same fingertip is picked up by a plurality of times, a fingerprint image or images on which the entire fingerprint image looks clearly cannot always be obtained, and it is often the case that each of the plurality of fingerprint images has some unclear portion. Accordingly, even if one of the plurality of fingerprint images on which the fingerprint looks most clearly is selected, it cannot be avoided that some unclear portions are included in the selected fingerprint image.
On the other hand, if a region in which a fingerprint looks clearly is clipped from each of a plurality of fingerprint images and such regions are synthesized to produce an image of the entire fingerprint, then the synthesis rather destroys the structure of fingerprint ridges and therefore makes the fingerprint image unclear. Particularly when two regions extracted from two different fingerprint images are synthesized, ridges in the regions cannot sometimes be connected well to each other, resulting in destruction of the ridge structure.
As described above, it is difficult to accurately extract characteristics unique to an individual from a fingerprint image which includes an unclear portion, and even if minutiae are extracted from such a fingerprint image as just described to produce registration fingerprint data, deterioration of the verification performance cannot be avoided.